Technical Field
The present invention relates to a semiconductor device, a driving mechanism and a motor driving control method.
Related Art
A technology is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 6-165568, that controls driving of a motor using a semiconductor device such as a microcontroller or the like. In JP-A No. 6-165568, a microcontroller, a driver circuit and a position detection circuit are used to control switching elements of a driving circuit (an upper arm and a lower arm) and control turning of a brushless motor.
In JP-A No. 2002-165476, a technology is disclosed that, without using a driver circuit, controls switching elements of a driving circuit (an upper arm and a lower arm), and controls turning of a motor and controls a power supply, with only a microcontroller and a position detection circuit.
In a motor, torque and the like is controlled by a current quantity flowing in a field coil in the motor. If, for some reason, control of the current flowing in the field coil becomes impossible, a serious accident may result. Therefore, when it becomes impossible to control current flowing in a field coil, current flowing in the field coil must be cut off immediately as a safety measure.
In general, if a motor is being driven and electrification of the motor stops while the motor is turning, current remaining in the coil produces a back electromotive force and the potential of a power supply is raised. When the potential of the power supply is raised, the withstand voltages of components connected to the power supply may be exceeded and these components may be damaged.
In order to solve this problem, in driving control of a brushless motor that uses a related art microcontroller, if an overcurrent in the brushless motor is detected and should be stopped, an interrupt is inputted from a comparator detecting the current to a central processing unit (CPU). Hence, a transistor of a lower arm that controls electrification between the brushless motor and ground is turned off, and a transistor of an upper arm that controls electrification between the brushless motor and a power supply is turned on. Thus, the two ends of the coil are short-circuited and the current is regenerated, induced current remaining in the coil is discharged, the back electromotive force is suppressed, and damage to components connected to the power supply is prevented.
However, in this case, processing of the interrupt from the comparator that detects the current must be processed in software by the CPU. Consequently, there is a time lag, the back electromotive force may not be suppressed immediately, and there is a danger of damage being caused to components by the back electromotive force.
JP-A No. 2007-028694 discloses a technology relating to a technology that controls driving of a three-phase AC motor by a rotary electric machine control device constituted with an integrated circuit. If, for some reason, it becomes impossible to control current flowing in the field coil of the rotary electric machine, the current flowing in the field coil is immediately cut off as a safety measure. Specifically, when it becomes impossible to control the current flowing in the field coil of the rotary electric machine for some reason, a PMOS transistor and an NMOS transistor that are connected in series with the field coil are cut off by control from the microcontroller.
Further still, JP-A No. 2003-335456 discloses a technology in which the value of a current flowing in a motor is compared with a pre-specified target current value by a comparator. If the value of the current flowing in the motor exceeds the target current value, control signals from a CPU are cut off and signals for controlling the value of current flowing in the motor are outputted directly to a driving circuit. Thus, when current changes are large reversals or the like, changes in current value relative to the target current value are suppressed.